The ability to predict an aircraft's trajectory is useful for several reasons. By trajectory, a four-dimensional description of the aircraft's path is meant. The description may be the evolution of the aircraft's state with time, where the state may include the position of the aircraft's centre of mass and other aspects of its motion such as velocity, attitude and weight.
For example, air traffic management (ATM) would benefit from an improved ability to predict an aircraft's four-dimensional trajectory. Air traffic management is responsible for the safe separation of aircraft, a particularly demanding task in congested airspace such as around airports. ATM decision-support tools based on accurate four-dimensional trajectory predictions could allow a greater volume of aircraft to be handled while maintaining safety.
The ability to predict an aircraft's four-dimensional trajectory will also be of benefit to the management of autonomous vehicles such as unmanned air vehicles (UAVs), for example in programming flight plans for UAVs as well as in commanding and de-conflicting their trajectories.
In order to predict an aircraft's four-dimensional trajectory unambiguously, one must solve a set of differential equations that model both aircraft behaviour and atmospheric conditions. Different sets of differential equations are available for use, some treating the aircraft as a six degrees of freedom of movement system and others treating the aircraft as a point mass with three degrees of freedom of movement. In addition, to solve the equations of motion, information concerning the aircraft's configuration is required as it will respond differently to control commands depending upon its configuration. Hence, further degrees of freedom of configuration may require definition that describe the configuration of the aircraft. For example, three degrees of freedom of configuration may be used to define landing gear configuration, speed brake configuration and lift devices configuration. Accordingly, aircraft intent may need to close six degrees of freedom to define an unambiguous trajectory, three degrees corresponding to motion of the aircraft in three axes and the other three degrees corresponding to aircraft configuration.
The computation process requires inputs corresponding to the aircraft intent, for example a description of aircraft intent expressed using a formal language. The aircraft intent provides enough information to predict unambiguously the trajectory that will be flown by the aircraft. The aircraft intent is usually derived from a description of flight intent, that is more-basic information that does not allow an unambiguous determination of aircraft trajectory. Aircraft intent may comprise information that captures basic commands, guidance modes and control inputs at the disposal of the pilot and/or the flight management system.
Aircraft intent must be distinguished from flight intent. Flight intent may be thought of as a generalisation of the concept of a flight plan, and so will reflect operational constraints and objectives such as an intended or required route and operator preferences. Generally, flight intent will not unambiguously define an aircraft's trajectory, as it is likely to contain only some of the information necessary to close all degrees of freedom. Put another way, there are likely to be many aircraft trajectories that could be calculated that would satisfy a given flight intent. Thus, flight intent may be regarded as a basic blueprint for a flight, but that lacks the specific details required to compute unambiguously a trajectory. Thus additional information must be combined with the flight intent to derive the aircraft intent that does allow an unambiguous prediction of the four-dimensional trajectory to be flown.
Aircraft intent is expressed using a set of parameters presented so as to allow equations of motion to be solved. The parameters may be left open (e.g. specifying a range of allowable parameters) or may be specified as a particular value. The former is referred to as an instance of parametric aircraft intent to distinguish it from the latter that is referred to as complete aircraft intent or just as aircraft intent. The theory of formal languages may be used to implement this formulation: an aircraft intent description language provides the set of instructions and the rules that govern the allowable combinations that express the aircraft intent, and so allow a prediction of the aircraft trajectory.
Co-pending U.S. patent application Ser. No. 12/679,275 published as US 2010-0305781 A1, also in the name of The Boeing Company, describes aircraft intent in more detail, and the disclosure of this application is incorporated herein in its entirety by reference. Co-pending U.S. patent application Ser. No. 13/360,318 published as US 2012-0290154 A1, also in the name of The Boeing Company, describes flight intent in more detail, and the disclosure of this application is incorporated herein in its entirety by reference.